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7. CALIBRATION
The ER3000 is fully calibrated at the factory.
temperature compensation and pressure linearization of the internal pressure sensor, and
linearization of both the analog setpoint and external feedback inputs. The additional
inputs and outputs on some models, as referenced in Section 3 (ER3000 Model
Description), are also linearized. The user is able to adjust the calibration as described in
the following sections.
7.1 Zero/span
The calibration of the unit may be changed by adjusting the zero and span settings of the
ER3000. The Zero and Span settings are found on the Miscellaneous Screen of the
Windows ER3000 program.
Normally, the zero and span do not need adjustment since the unit has been factory
calibrated. However, under the following conditions it may be advantageous to make
some adjustment:
•
The application is using a reduced pressure range.
•
The unit is normally operating under nonstandard temperature conditions
and it is desired to optimize the calibration for this environment.
•
There has been some long-term drift in the calibration.
•
An external transducer is being used to provide feedback.
The procedure is as follows:
1. Connect a reference pressure gauge to the output of the ER3000 (or the
output of the booster regulator, if one is being used).
2. Set the setpoint (via the analog setpoint input or the RS485 interface as
appropriate) to a value close to zero (4.16 mA for analog input or 1% for
RS485 interface are recommended).
3. If the reference pressure meter does not indicate 1 psi then increase the zero
value to raise the reading or decrease to lower it, as required.
4. Next, set the setpoint to a value close to 100% (19.2 mA for the analog
setpoint or 95% for RS485 interface are good values).
5. If the reference pressure meter does not indicate 95 psi then increase the
span value to raise the reading or decrease to lower it, as required.
6. Set the setpoint (via the analog setpoint input or the RS485 interface as
appropriate) to a value close to zero (4.16 mA for analog input or 1% for
RS485 interface are recommended).
7. Verify that the pressure meter indicates 1 psi. If not, then repeat above
procedure.
A couple of points should be noted for proper calibration. First, the controller should be
properly tuned before performing calibration, if possible. Second, proper time for the
pressure to settle to a stable value should be allowed for each step. Finally, if the zero is
adjusted too far in the negative direction, then the output will not respond until the zero
is raised to within the control range (i.e. - so that the output is above zero psi).
The calibration process involves
7. Calibration 39
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